Low temperature liquid storage devices

ABSTRACT

1,210,624. Liquefied gas storage containers; cryostats. MAX-PLANCK-GES ZUR FORDERUNG DER WISSENSCHAFTEN E.V. 6 Feb., 1969 [13 Feb., 1968], No. 6593/69. Headings F4H and F4P. A radiation shield surrounding a vessel containing a liquefied gas is cooled by a heat exchanger which is fed with exhaust gas from the vessel and which has an internal crosssection larger than that of the pipe leading the gas to it. The vessel may be a cryostat or a reservoir for supplying a cryostat. As illustrated, the radiation shield contacts a heat exchanger whose internal wall has a helical element 3 which, together with a plug 15 defines a helical flow path for the exhaust gas flowing in a pipe 4. If it is necessary to introduce inserts into the vessel through the pipe 4 the plug 15 may be omitted. In this case, a pipe for the inserts may be enclosed within the pipe 4 and be contacted by the helical element 3, the exhaust gas then flowing in the annular space between the two pipes. In an alternative form of heat exchanger, Fig. 4 (not shown), the helical element is omitted and a sintered metal plug fills the transverse cross-section of the heat exchanger.

Nov, 10, 1970 G. KLING ET 5 LOW TEMPERATURE LIQUID STORAGE DEVICES FiledFeb. 12, 1969 5 Sheets-Sheet 1 Fig.1

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Nov. 10, 1970 cs. KLING ET AL 3,538,714

LOW TEMPERATURE LIQUID STORAGE DEVICES Filed Feb. 12, 1969 3Sheets-Sheet 2 Fig. .3

I Inventors: KL 3 Hun DaL ex Rttornass ited States 3,538,714 LOWTEMPERATURE LIQUID STORAGE DEVICES Gustav Klipping, Frithjof Schmidt,and Harry Walter, Berlin, Germany, assignors to Max-Planck-Gesellschaftzur Forderung der Wisscnschaften e.V., Gottingen, Germany Filed Feb. 12,1969, Ser. No. 798,754 Claims priority, application Germany, Feb. 13,1968, 1,601,908 Int. Cl. F17c 13/00 US. Cl. 6254 8 Claims ABSTRACT OFTHE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relatesto the cooling of radiation shields in vessels and apparatus containinglow-boiling liquids as coolants, and particularly to the cooling ofradiation shields by establishing a heat-conducting connection withportions of the waste gas line of such apparatus.

Storage vessels for liquid helium are known in which a vacuum-insulatedinner container is enclosed by a plurality of protective shields. Theshields are supported by the neck tube of the container and are cooledvia their metallic connection with this tube; such cooling beingeifected by utilizing the heat absorbing capacity of the evaporated gas.This idea is described, for example, in the following:

A. A. Balla, E. Donth, Experimental Technique in 'Physics XIII (1965)pages 184-190, VEB Deutscher Verlag der Wissenschaf-Leipzig; O. P.Anashkin, I. B. Danilov, V. G. Krvenko, Cryogenics 6 (1966) pages106-107, Heywood-Temple, Industrial Publications Ltd., London; Germanpublished patent application No. 1,23 0,- 048; V. E. Keilin, Cryogenics7 (1967) pages 3 to 6, FIG. 1.

These known arrangements exhibit the drawback of not fully utilizing theheat absorbing capabiilty of the exhaust, or waste, gases, particularlyin the case of a large supply of gas, primarily because the heattransfer rate between the exhaust gas line and the radiation shieldsremains quite low. It has also been disclosed, in German Pat. No.1,151,264, to conduct the exhaust gases from a continuous-flow cryostatthrough a helically wound pipe which encloses the evaporator body toform a radiation shield. Such an arrangement results in a substantialimprovement in the degree of utilization of the heat absorbing capacityof the exhaust gases. But it also gives rise to an undesirable increasein the flow resistance presented by the exhaust gas line.

SUMMARY OF THE INVENTION It is a primary object of the present inventionto overcome these drawbacks and difficulties.

Another object of the invention is to substantially improve theefficiency of the cooling action effected by the waste gas.

Still another object of the invention is to provide a more efiicientheat exchange between the associated radiation shields and the wastegas.

atent Still another object of the invention is to provide an improvedheat exchange without increasing the flow resistance of the waste gasline.

These and other objects are achieved by the provision of an improvedheat exchange element in combination with apparatus for storing a lowtemperature liquid. This apparatus includes a container for such liquid,a waste gas pipe connected to the container and communicating with theinterior thereof, and a radiation shield surrounding the container andconnected to the pipe in a heat conductive manner for permitting atleast part of the shield to be cooled. The heat exchange elementaccording to the invention is connected in series in the pipe to betraversed by the gas flowing through the pipe, the element presenting agas flow path whose cross-sectional area is greater than that of the gasflow path defined by the pipe and having an outer surface contacting theshield and defining the surface via which heat is transferred from theshield.

Thus, the present invention provides a device for cooling radiationshields in which favorable heat transfer conditions are created andwhich can be manufactured, installed and disassembled in a simplemanner. Moreover, heat exchange elements according to the invention donot create any noticeable increase in the gas flow resistance of thewaste gas pipe.

Heat exchange elements according to the invention are highlyadvantageous because, even when the waste gas pipe is relatively short,these elements serve to substantially enlarge the effective heatexchange area, which results in a corresponding increase in the rate atwhich heat can be exchanged with the radiation shields.

In preferred embodiments of the invention, the heat exchanger isconstructed so that its gas flow region is provided with gas conduitsformed in a heat conductive ma terial and presenting a gas flow regionwhich is symmetrical with respect to the longitudinal axis of theexchanger. Preferably, the interior of the exchanger has the form of ahelical conduit.

According to one form of construction of embodiments of the invention,the unobstmcted cross section of the heat exchanger gas flow region,which is in the form of a cylinder defining the inner boundary of theconduit, has a cross-sectional area equal to, and coaxial with, thecross-sectionl area of the interior of the waste gas pipe.

The dimensioning of the heat exchanger to cause it to have anunobstructed cross section which is equal to that of the waste gas pipeis advantageous because it assures that standardized siphons can beinserted through both the pipe and the heat exchanger.

According to a further form of construction of embodiments of theinvention, there is also provided a further pipe which extends throughthe heat exchanger and partially through the waste gas pipe, the furtherpipe having a smaller cross-sectional area than the waste gas pipe sothat the two pipes define an annular gas flow path, and being connectedto the helical conduit which has an unobstructed cross section ofsmaller diameter than the cross section of the waste gas pipe. Theprovision of this further pipe assures that there will be a clearpassage for the insertion of probes, siphons, samples, etc., andfurthermore all of the waste gas is forced to pass the helical gasconduit even if no probe or something else is inserted.

In those cases when it is not necessary to provide the capability ofpermitting instruments to be inserted through the waste gas pipe, itmight prove desirable to plug the unobstructed central region of theheat exchanger so as to force all of the waste gas to traverse thehelical gas conduit. This can be accomplished by means of a solid plugof heat conducting material which is axially coextensive with thehelical conduit.

In other forms of construction according to the invention, the heatexchange element can be constituted by a sintered metal packing disposedwithin a hollow jacket and extending across the entire cross-sectionalarea of the hollow region defined by the jacket, the packing beingdimensioned to cause the jacket to also present a gas distributionchamber at each end of the packing. Arrangements of this type are highlyadvantageous because they permit optimum heat exchange conditions to beachieved.

In further accordance with the invention, the radiation shields whichare to be cooled are formed with a socket-type sleeve into which a heatexchanger according to the invention can be tightly inserted in such amanner as to cause the outer surface of the heat exchanger to be inclose heat-exchanging contact with the socket. This arrangementsubstantially simplifies installation of the heat exchanger and permitsexcellent heat transfer conditions to be established.

In further accordance with the invention, when a plurality of heatexchangers are inserted along the length of the waste gas pipe, it mightprove advantageous to dimension the individual lengths of the waste gaspipe and the individual heat exchangers so as to provide a progressiveincrease in the cross-sectional area of the gas flow path in thedirection of gas flow. This compensates for the tendency of the wastegas to expand each time it is heated and thus maintains the flowresistance of the waste gas line at a low value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view ofone embodiment of a heat exchanger according to the invention.

FIG. 2 is a simplified pictorial illustration of a storage vesselconstructed according to the invention.

FIG. 3 is a view similar to that of FIG. 1 of another embodiment of theinvention.

FIG. 4 is a view similar to that of FIG. 1 of still another embodimentof the invention.

FIG. 5 is a view similar to that of FIG. 2 of a continuous-flow cryostatconstructed according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment shown in FIG.1, the heat exchanger 1 consists of a cylindrical hollow body 2 whoseinner wall is formed to create a helical, heat-conductive gas conduit 3which, it should be noted, does not extend along the entire length ofthe inner wall, and which defines a gas fiow channel 3. The heatexchanger 1 is made, for example, of copper and is interposed as anintermediate piece in the thin-walled waste gas pipe 4 made of amaterial having a low thermal conductivity and high structural strength,one such material being refined steel.

A radiation shield 6 provided with an integral plugtype sleeve 5 isconnected to the outside of the heat exchanger 1 in such a way that theentire external surface of the heat exchanger 1 is in good heat exchangecontact with the radiation shield 6.

The unobstructed cross section of the heat exchanger 1, which is acylindrical region defining the inner boundary of channel 3' correspondswith the cross section of the waste gas pipe 4, so that, for example, asiphon, or probe, or the like, can pass through the heat exchanger 1 forinsertion into the inner container. After a siphon whose diameter issomewhat smaller than the diameter of the waste gas pipe 4 has beeninserted, an annular gap results between the siphon jacket pipe and thepipe 4, this ,gap being interrupted by heat exchanger 1, and it isthrough this gap that the waste gas flows. If no siphon 4 were inserted,the full cross section of the gas pipe 4 would be available for the flowof exhaust gas.

FIG. 2 shows a variant of the heat exchanger illustrated in FIG. 1 inassociation with a storage can 7 having two radiation shields 8 and 9surrounding an inner vessel 12 containing a coolant 11. There are twoheat exchangers 1a, 1b each having the form of a hollow body presentinga helical gas conduit as shown in FIG. 1. However, the heat exchangersare here of smaller unobstructed cross section than in FIG. 1 and aretraversed by an inner pipe 10 which is connected to the inner boundaryof the gas conduits 3.

The inner pipe 10 extends from below the heat exchanger 1a, which isconnected to the innermost shield 9, to the outer end of the gas pipe 4,pipe 4 here constituting the neck tube of inner vessel 12, and isenclosed by the waste gas pipe 4. Between the inner pipe 10 and the gaspipe 4 there is thus created an annular gap which is interrupted by thetwo heat exchangers 1a and 1b and through which the waste gas flowstoward the waste gas discharge connection 13.

This embodiment presents the advantage that the waste gas will be fedthrough a narrow annular gap even when no siphon is present and that theentire mass of waste gas is forced to flow substantially through thehelical conduits of the heat exchangers la and 1b. Upon removal of asiphon, the upper end of inner pipe 10 is closed by a cover or stopper14.

This arrangement is of particular interest when large amounts of wastegas develop, for example in storage vessels having large capacities.

FIG. 3 shows another embodiment of the heat exchanger according to theinvention which is advantageously employed in those cases where nothingneed be inserted through the waste gas pipe. The free cylindrical regionenclosed by, and defining the inner boundary of, the helical gas conduit3 is here closed off by a permanently inserted solid heat-conductingplug 15 which extends over the entire length of the helical conduit. Atthe gas inlet side of the heat exchanger there is provided a gasdistribution chamber 17 within the heat exchanger. A similar chamber 16is provided at the gas outlet side. This embodiment also serves to causethe entire mass of Waste gas to flow through the heat exchanger helicalconduit.

FIG. 4 shows an embodiment of the heat exchanger in which asintered-metal packing 18 is inserted in a closed cylindrical hollowbody, made of two parts 2a and 2b, to serve as the heat-exchangeelement. In this embodiment optimum heat exchange-conditions can berealized since, as is known, sintered-metal bodies present a very largeinternal surface and good thermal conductivity. Appropriatesintered-metal packings could also be used in the embodiment illustratedin FIG. 2. Materials suited for the sintered-metal packing are copper,silver, aluminum, bronze and the like.

FIG. 5 is a schematic representation of a continuousflow cryostat inwhich heat exchangers of the type illustrated in FIG. 4 are used. Theevaporator cooling head 20, supplied with coolant through a feed line19, holds a probe 21 and is enclosed on all sides by two radiationshields 22 and 23. The radiation shields 22 and 23 are inheat-conductive communication with the heat exchangers 24 and 25,respectively, disposed in series with the waste gas pipe 4 of evaporator20. The entire apparatus is enclosed in an evacuatable housing 26. Theheat exchangers illustrated in FIGS. 3 and 4 are the most advantageousembodiments to he employed in this apparatus.

Such a continuous-flow cryostat is distinguished by a particularlysimple construction. The exhaust gas pipe may be constructed of sectionshaving progressively increasing cross-sectional areas corresponding tothe decreasing density of the gas, thus keeping the flow resist ance ofthe waste gas pipe at a low value. Moreover,

suitable dimensioning of the heat exchangers permits a truly completeutilizatiton of the heat absorbing capacity of the gas to be achieved.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations.

We claim:

1. In combination with apparatus for storing a low temperature liquidand including a container for such liquid, a waste gas pipe connected tothe container and communicating with the interior thereof, and aradiation shield surrounding the container and connected to the pipe ina heat conductive manner for permitting at least part of the shield tobe cooled, the improvement comprising: a heat exchange element connectedin series in said pipe to be traversed by the gas flowing through saidpipe, said element being a hollow body whose cross-sectional area isgreater than that of the gas flow path defined by said pipe and havingan outer Wall contacting said shield and defining the surface via whichheat is transferred from said shield; and gas flow directing meansdisposed in said hollow body adjacent said outer wall and constructedfor deflecting at least that part of the gas flowing adjacent the innersurface of said outer wall to cause such gas to follow a flow paththrough said element which is longer than the axial length of saidelement.

2. An arrangement as defined in claim 1 wherein said directing meanscomprise at least one heat-conductive gas conduit which defines the gasflow path and wherein said element is symmetrical with respect to itslongitudinal axis.

3. An arrangement as defined in claim 2 wherein there is a singlehelical gas conduit.

4. An arrangement defined in claim 3 wherein the inner boundary of saidgas conduit defines a hollow cylindrical region and having a crosssection which is equal to, and coaxial with, the internal cross sectionof said waste gas pipe.

5. An arrangement as defined in claim 3 wherein the inner boundary ofsaid conduit defines a hollow cylindrical region, and said elementcomprises a solid plug of heat conductive material completely fillingsaid hollow cylindrical region and coextensive with said helicalconduit.

6. An arrangement as defined in claim 2 further comprising an inner pipepassing completely through said heat exchanger and at least partiallythrough said waste gas pipe, the external diameter of said inner pipebeing less than the internal diameter of said waste gas pipe and saidinner pipe and waste gas pipe defining between them an annular gas flowregion, and said inner pipe being connected to the inner boundarysurface of said heat exchanger having an unobstructed cross section ofless than the internal diameter of said waste gas pipe.

7. An arrangement as defined in claim 1 wherein said radiation shield isformed with an integral hollow sleeve in which said heat exchangeelement is tightly inserted.

8. An arrangement as defined in claim 1 wherein there are a plurality ofheat exchange elements connected in series in said pipe and dividingsaid pipe into a plurality of sections, the internal cross-sectitonalareas of said pipe sections and said heat exchange elements increasingprogressively in the direction of waste gas flow.

References Cited UNITED STATES PATENTS 2,643,022 6/1953 Cornell 220-153,097,084 7/1963 Putman 220-14 X 3,133,422 5/1964 Paivanas 62-503,341,052 9/1967 Barthel 220-14 ALBERT W. DAVIS, JR., Primary ExaminerUS. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,538,714 Dated November 10th, 1970 Inventor(s) Gustav Klipping, FrithjofSchmidt and Harry Walte It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading of drawing sheets 1 2 and 3 respectively, change thepatentee 5 name to -G Klipping et a1 Column 1, line 50, change"capabiilty" to --capability-. Column 5, line 2, change "utilizatiton"to -utilization. Column 6, line 23, change "sectitonal" to -sectional-.

SKiNED A SEALED FEB 9 Mlnacbe -I mm 3. W, I Ii 0mm muonsof Patna

